Question: Express this number in scientific notation. $0.000\;639\;7$
Solution: Count the zeroes to the right of the decimal point before the leading $\leadingColor{6}$ : there are $3$ zeroes If you count the leading digit $\leadingColor{6}$ and those zeroes , there are $\exponentColor{4}$ digits to the right of the decimal point. So: $0.000\;639\;7 = \leadingColor{6}.397 \times 10^{\exponentColor{-4}}$